Implementing Tunnels

This module describes the various types of tunneling techniques available using Cisco IOS software. Configuration details and examples are provided for the tunnel types that use physical or virtual interfaces. Many tunneling techniques are implemented using technology-specific commands, and links are provided to the appropriate technology modules.

Tunneling provides a way to encapsulate arbitrary packets inside a transport protocol. Tunnels are implemented as a virtual interface to provide a simple interface for configuration. The tunnel interface is not tied to specific "passenger" or "transport" protocols, but rather is an architecture to provide the services necessary to implement any standard point-to-point encapsulation scheme.

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest caveats and feature information, see
Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the feature information table at the end of this module.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to
www.cisco.com/​go/​cfn. An account on Cisco.com is not required.

Prerequisites for Implementing Tunnels

This module assumes that you are running Cisco IOS Release 12.2 software or a later release.

Restrictions for Implementing Tunnels

In early versions of Cisco IOS software, only processor switching was supported. Fast switching of GRE tunnels was introduced in Cisco IOS Release 11.1. Cisco Express Forwarding (CEF) switching is also now commonly used by the IPv6 and other tunneling protocols.

It is important to allow the tunnel protocol through a firewall and to allow it to pass access control list (ACL) checking.

Multiple point-to-point tunnels can saturate the physical link with routing information if the bandwidth is not configured correctly on the tunnel interface.

A tunnel looks like a single hop, and routing protocols may prefer a tunnel over a multihop physical path. This can be deceptive because the tunnel, although it may look like a single hop, may traverse a slower path than a multihop link. A tunnel is as robust and fast, or as unreliable and slow, as the links that it actually traverses. Routing protocols that make their decisions on the sole basis of hop count will often prefer a tunnel over a set of physical links. A tunnel might appear to be a one-hop, point-to-point link and have the lowest-cost path, but may actually cost more in terms of latency than an alternative physical topology. For example, in the topology shown in the figure below, packets from Host 1 will appear to travel across networks w, t, and z to get to Host 2 instead of taking the path w, x, y, and z because the tunnel hop count appears shorter. In fact, the packets going through the tunnel will still be traveling across Router A, B, and C, but they must also travel to Router D before coming back to Router C.

Figure 1. Tunnel Precautions: Hop Counts

If routing is not carefully configured, the tunnel may have a recursive routing problem. When the best path to the "tunnel destination" is via the tunnel itself, recursive routing causes the tunnel interface to flap. To avoid recursive routing problems, keep the control-plane routing separate from the tunnel routing using the following methods:

Use a different autonomous system number or tag.

Use a different routing protocol.

Use static routes to override the first hop (but watch for routing loops).

When you have recursive routing to the tunnel destination, the following error is displayed:

You cannot configure an IP tunnel or a GRE tunnel on Cisco 7600 series routers which has an MPLS Traffic Engineering (TE) tunnel as the egress path, because the configuration results in forwarding loops.

Tunneling Versus Encapsulation

To understand how tunnels work, it is important to distinguish between the concepts of encapsulation and tunneling. Encapsulation is the process of adding headers to data at each layer of a particular protocol stack. The Open Systems Interconnection (OSI) reference model describes the functions of a network as seven layers stacked on top of each other. When data has to be sent from one host (a PC for example) on a network to another host, the process of encapsulation is used to add a header in front of the data at each layer of the protocol stack in descending order. The header must contain a data field that indicates the type of data encapsulated at the layer immediately above the current layer. As the packet ascends the protocol stack on the receiving side of the network, each encapsulation header is removed in the reverse order.

Tunneling encapsulates data packets from one protocol inside a different protocol and transports the data packets unchanged across a foreign network. Unlike encapsulation, tunneling allows a lower-layer protocol, or same-layer protocol, to be carried through the tunnel. A tunnel interface is a virtual (or logical) interface. For more details on other types of virtual interfaces, see the "Configuring Virtual Interfaces" module. Although many different types of tunnels have been created to solve different network problems, tunneling consists of three main components:

Passenger protocol--The protocol that you are encapsulating. Examples of passenger protocols are AppleTalk, connectionless network service (CLNS), IP, and IPX.

Transport protocol--The protocol used to carry the encapsulated protocol. The main transport protocol is IP.

To understand the process of tunneling, consider connecting two AppleTalk networks with a non-AppleTalk backbone, such as IP. The relatively high bandwidth consumed by the broadcasting of Routing Table Maintenance Protocol (RTMP) data packets can severely hamper the backbone’s network performance. This problem can be solved by tunneling AppleTalk through a foreign protocol, such as IP. Tunneling encapsulates an AppleTalk packet inside the foreign protocol packet (AppleTalk inside GRE inside IP), which is then sent across the backbone to a destination router. The destination router then removes the encapsulation from the AppleTalk packet and routes the packet.

Definition of Tunneling Types by OSI Layer

Tunnels are used by many different technologies to solve different network challenges, and the resulting variety of tunnel types makes it difficult to determine which tunneling technique to use. The different carrier protocols can be grouped according to the OSI layer model. The table below shows the different carrier protocols grouped by OSI layer. Below the table, each carrier protocol is defined, and if the tunnel configuration is not covered within this module, a link to the appropriate module is included.

Table 1 Carrier Protocol by OSI Layer

Layer

Carrier Protocol

2

PPPoA--Point-to-Point Protocol (PPP) over ATM

PPPoE--PPP over Ethernet

UDLR--Unidirectional link routing

3

BSTUN--Block Serial Tunneling

CLNS--Connectionless Network Service (CLNS)

GRE--Generic routing encapsulation

IP-in-IP--Internet Protocol encapsulated within IP

IPsec--IP Security

IPv6--IP version 6

L2F--Layer 2 Forwarding

L2TP--Layer 2 Tunneling Protocol

MPLS--Multiprotocol Label Switching

PPTP--Point-to-Point Tunneling Protocol

STUN--Serial Tunneling

4

DLSw+--Data-link switching plus

RBSCP--Rate-Based Satellite Control Protocol

SSL--Secure Socket Layer

BSTUN

A Block Serial Tunnel (BSTUN) enables support for devices using the Bisync data-link protocol. This protocol enables enterprises to transport Bisync traffic over the same network that supports their Systems Network Architecture (SNA) and multiprotocol traffic, eliminating the need for separate Bisync facilities.

For more details about configuring BSTUN, see the "Configuring Serial Tunnel and Block Serial Tunnel" module in the Cisco IOS Bridging and IBM Networking Configuration Guide.

CLNS

The ISO Connectionless Network Service (CLNS) protocol is a standard for the network layer of the OSI model. IP traffic can be transported over CLNS; for instance, on the data communications channel (DCC) of a SONET ring. An IP over CLNS tunnel (CTunnel) is a virtual interface that enhances interactions with CLNS networks, allowing IP packets to be tunneled through the Connectionless Network Protocol (CLNP) to preserve TCP/IP services. CLNS can also be used as a transport protocol with GRE as a carrier protocol (GRE/CLNS), carrying both IPv4 and IPv6 packets.

DLSw+

Data-link switching plus (DLSw+) is Cisco’s implementation of the DLSw standard for Systems Network Architecture (SNA) and NetBIOS devices, and it supports several additional features and enhancements. DLSw+ is a means of transporting SNA and NetBIOS traffic over a campus or WAN. The end systems can attach to the network over Token Ring, Ethernet, Synchronous Data Link Control (SDLC), Qualified Logical Link Control (QLLC), or Fiber Distributed Data Interface (FDDI). DLSw+ switches between diverse media and locally terminates the data links, keeping acknowledgments, keepalives, and polling off the WAN.

For more details about configuring DLSw+, see the "Configuring Data-Link Switching Plus" module in the Cisco IOS Bridging and IBM Networking Configuration Guide .

GRE

Generic routing encapsulation (GRE) is defined in RFC 2784. GRE is a carrier protocol that can be used with a variety of underlying transport protocols, and GRE can carry a variety of passenger protocols. RFC 2784 also covers the use of GRE with IPv4 as the transport protocol and the passenger protocol. Cisco IOS software supports GRE as the carrier protocol with many combinations of passenger and transport protocols.

IP-in-IP

IP-in-IP is a Layer 3 tunneling protocol--defined in RFC 2003--that alters the normal routing of an IP packet by encapsulating it within another IP header. The encapsulating header specifies the address of a router that would not ordinarily be selected as a next-hop router on the basis of the real destination address of the packet. The intermediate node decapsulates the packet, which is then routed to the destination as usual.

IPsec

In simple terms, IP Security (IPsec) provides secure tunnels between two peers, such as two routers. You define which packets are considered sensitive and should be sent through these secure tunnels, and you define the parameters that should be used to protect these packets by specifying characteristics of these tunnels. IPsec peers set up a secure tunnel and encrypt the packets that traverse the tunnel to the remote peer.

IPsec also works with the GRE and IP-in-IP, L2F, L2TP, and DLSw+ tunneling protocols; however, multipoint tunnels are not supported. Other Layer 3 tunneling protocols may not be supported for use with IPsec.

For more details about configuring IPSec, see the "Configuring Security for VPNs with IPSec" module in the Cisco IOS Security Configuration Guide.

IPv6

IP version 6 (IPv6) is a new version of the Internet Protocol based on and designed as the successor to IP version 4. IPv6 adds a much larger address space--128 bits--and improvements such as a simplified main header and extension headers. IPv6 is described initially in RFC 2460,
Internet Protocol, Version 6 (IPv6) . The use of IPv6 as a carrier protocol is described in RFC 2473,
Generic Packet Tunneling in IPv6 Specification .

L2F

Layer 2 Forwarding (L2F) tunneling is used in virtual private dialup networks (VPDNs). A VPDN allows separate and autonomous protocol domains to share common access infrastructure including modems, access servers, and ISDN routers by the tunneling of link-level (Layer 2) frames. Typical L2F tunneling use includes Internet service providers (ISPs) or other access service creating virtual tunnels to link to remote customer sites or remote users with corporate intranet or extranet networks.

L2TP

Layer 2 Tunneling Protocol (L2TP) is an open standard created by the Internet Engineering Task Force (IETF) that uses the best features of L2F and Point-to-Point Tunneling Protocol (PPTP). L2TP is designed to secure the transmission of IP packets across uncontrolled and untrusted network domains, and it is an important component of Virtual Private Networks (VPNs). VPNs extend remote access to users over a shared infrastructure while maintaining the same security and management policies as a private network.

For more details about configuring L2TP, see the Cisco IOS Dial Technologies Configuration Guide.

MPLS

Multiprotocol Label Switching (MPLS) is a high-performance packet forwarding technology that integrates the performance and traffic management capabilities of data-link-layer (Layer 2) switching with the scalability, flexibility, and performance of network-layer (Layer 3) routing. The MPLS architecture has been designed to allow data to be transferred over any combination of Layer 2 technologies, to support all Layer 3 protocols, and to scale. Using CEF, MPLS can efficiently enable the delivery of IP services over an ATM switched network. MPLS is an integration of Layer 2 and Layer 3 technologies. By making traditional Layer 2 features available to Layer 3, MPLS enables traffic engineering.

For more details about how MPLS traffic engineering uses tunnels, see the Cisco IOS Multiprotocol Label Switching Configuration Guide.

PPPoA

PPP over ATM (PPPoA) is mainly implemented as part of Asymmetric Digital Subscriber Line (ADSL). It relies on RFC 1483, operating in either Logical Link Control-Subnetwork Access Protocol (LLC-SNAP) or VC-Mux mode. A customer premises equipment (CPE) device encapsulates the PPP session based on this RFC for transport across the ADSL loop and the digital subscriber line access multiplexer (DSLAM).

PPPoE

RFC 2516 defines PPP over Ethernet (PPPoE) as providing the ability to connect a network of hosts over a simple bridging access device to a remote access concentrator or aggregation concentrator. As customers deploy ADSL, they must support PPP-style authentication and authorization over a large installed base of legacy bridging customer premises equipment (CPE). Using a form of tunneling encapsulation, PPPoE allows each host to use its own PPP stack, thus presenting the user with a familiar user interface. Access control, billing, and type of service (ToS) can be done on a per-user, rather than a per-site, basis.

For more details about configuring PPPoE, see the Cisco IOS Broadband Access Aggregation and DSL Configuration Guide.

PPTP

Point-to-Point Tunneling Protocol (PPTP) is a network protocol that enables the secure transfer of data from a remote client enterprise server by creating a VPN across TCP/IP data networks. PPTP supports on-demand, multiprotocol virtual private networking over public networks such as the Internet.

RBSCP

Rate-Based Satellite Control Protocol (RBSCP) was designed for wireless or long-distance delay links with high error rates, such as satellite links. Using tunnels, RBSCP can improve the performance of certain IP protocols, such as TCP and IP Security (IPsec), over satellite links without breaking the end-to-end model.

SSL Tunnels

Secure Socket Layer (SSL) is designed to make use of TCP sessions to provide a reliable end-to-end secure service. The main role of SSL is to provide security for web traffic. Security includes confidentiality, message integrity, and authentication. SSL achieves these elements of security through the use of cryptography, digital signatures, and certificates. SSL protects confidential information through the use of cryptography. Sensitive data is encrypted across public networks to achieve a level of confidentiality.

STUN

Cisco’s Serial Tunneling (STUN) implementation allows Synchronous Data Link Control (SDLC) protocol devices and High-Level Data Link Control (HDLC) devices to connect to one another through a multiprotocol internetwork rather than through a direct serial link. STUN encapsulates SDLC frames in either the TCP/IP or the HDLC protocol. STUN provides a straight passthrough of all SDLC traffic (including control frames, such as Receiver Ready) end-to-end between Systems Network Architecture (SNA) devices.

UDLR Tunnels

Unidirectional link routing (UDLR) provides mechanisms for a router to emulate a bidirectional link to enable the routing of unicast and multicast packets over a physical unidirectional interface, such as a broadcast satellite link. However, there must be a back channel or other path between the routers that share a physical unidirectional link (UDL). A UDLR tunnel is a mechanism for unicast and multicast traffic; Internet Group Management Protocol (IGMP) UDLR is a related technology for multicast traffic.

For more details, see Cisco IOS IP Multicast Configuration Guide.

Benefits of Tunneling

The following are several situations in which tunneling (encapsulating traffic in another protocol) is useful:

To enable multiprotocol local networks over a single-protocol backbone.

To provide workarounds for networks that use protocols that have limited hop counts; for example, RIP version 1, AppleTalk (see the figure below).

To connect discontiguous subnetworks.

To allow virtual private networks across WANs.

Figure 2. Providing Workarounds for Networks with Limited Hop Counts

Tunnel ToS

Tunnel ToS allows you to tunnel your network traffic and group all your packets in the same specific ToS byte value. The ToS byte values and Time-to-Live (TTL) hop-count value can be set in the encapsulating IP header of tunnel packets for an IP tunnel interface on a router. The Tunnel ToS feature is supported for CEF, fast switching, and process switching.

The ToS and TTL byte values are defined in RFC 791. RFC 2474 and RFC 2780 obsolete the use of the ToS byte as defined in RFC 791. RFC 791 specifies that bits 6 and 7 of the ToS byte (the first two least significant bits) are reserved for future use and should be set to 0. The Tunnel ToS feature does not conform to this standard and allows you to set the whole ToS byte value, including bits 6 and 7, and to decide to which RFC standard the ToS byte of your packets should confirm.

Mobile IP Tunneling

New devices and business practices, such as PDAs and the next-generation of data-ready cellular phones and services, are driving interest in the ability of a user to roam while maintaining network connectivity. The requirement for data connectivity solutions for this group of users is very different than it is for the fixed dialup user or the stationary wired LAN user. Solutions need to accommodate the challenge of movement during a data session or conversation.

Mobile IP is comprises the following three components, as shown in the figure below:

Mobile node (MN)

Home agent (HA)

Foreign agent (FA)

Figure 3. Mobile IP Components and Use of Tunneling

An MN is a node, for example, a PDA, a laptop computer, or a data-ready cellular phone, that can change its point of attachment from one network or subnet to another. This node can maintain ongoing communications while using only its home IP address. In the figure above, the current location of the MN--a laptop computer--is shown in bold.

An HA is a router on the home network of the MN that maintains an association between the home IP address of the MN and its
care-of address , which is the current location of the MN on a foreign or visited network. The HA redirects packets by tunneling them to the MN while it is away from home.

An FA is a router on a foreign network that assists the MN in informing its HA of its current care-of address. The FA detunnels packets that were tunneled by the HA and delivers them to the MN. The FA also acts as the default router for packets generated by the MN while it is connected to the foreign network.

The traffic destined for the MN is forwarded in a triangular manner. When a device on the Internet, called a correspondent node (CN), sends a packet to the MN, the packet is routed to the home network of the MN, the HA redirects the packet by tunneling to the care-of address (current location) of the MN on the foreign network, as shown in the figure above. The FA receives the packet from the HA and forwards it locally to the MN. However, packets sent by the MN are routed directly to the CN.

For more details about configuring Mobile IP, see the Cisco IOS IP Mobility Configuration Guide.

Generic Routing Encapsulation

Generic routing encapsulation (GRE) is defined in RFC 2784. GRE is a carrier protocol that can be used with a variety of underlying transport protocols and that can carry a variety of passenger protocols. RFC 2784 also covers the use of GRE with IPv4 as the transport protocol and the passenger protocol. Cisco IOS software supports GRE as the carrier protocol with many combinations of passenger and transport protocols such as:

The following descriptions of GRE tunnels are included:

GRE Tunnel IP Source and Destination VRF Membership

GRE Tunnel IP Source and Destination VRF Membership allows you to configure the source and destination of a tunnel to belong to any VRF tables. A VRF table stores routing data for each VPN. The VRF table defines the VPN membership of a customer site attached to the network access server (NAS). Each VRF table comprises an IP routing table, a derived CEF table, and guidelines and routing protocol parameters that control the information that is included in the routing table.

Previously, Generic Routing Encapsulation (GRE) IP tunnels required the IP tunnel destination to be in the global routing table. The implementation of this feature allows you to configure a tunnel source and destination to belong to any VRF. As with existing GRE tunnels, the tunnel becomes disabled if no route to the tunnel destination is defined.

EoMPLS over GRE

Ethernet over multiprotocol label switching (EoMPLS) is a tunneling mechanism that allows you to tunnel Layer 2 traffic through a Layer 3 MPLS network. EoMPLS is also known as Layer 2 tunneling.

EoMPLS effectively facilitates the Layer 2 extension over long distances. EoMPLS over GRE helps to create the GRE tunnel as hardware-based switched, and with high performance that encapsulates EoMPLS frames within the GRE tunnel. The GRE connection is established between the two core routers, and then the MPLS LSP is tunneled over.

GRE encapsulation is used to define a packet that has some additional header information added to it prior to being forwarded. De-encapsulation is the process of removing the additional header information when the packet reaches the destination tunnel endpoint.

When a packet is forwarded through a GRE tunnel, two new headers are appended at the front of the packet and hence the context of the new payload changes. After encapsulation, what was originally the data payload and separate IP header is now known as the GRE payload. A GRE header is added to the packet to provide information on the protocol type and also a recalculated checksum. Also, a new IP header is added to the front of the GRE header. This IP header contains the destination IP address of the tunnel.

The GRE header is appended to the packet (IP, L2VPN, L3VPN, etc.) before entering the tunnel. All routers along the path that receive the encapsulated packet will use the new IP header to determine where to send the packet in an effort for it to reach the tunnel endpoint.

In the IP forwarding case on reaching the tunnel destination endpoint, the new IP header and GRE header are removed from the packet and the original IP header is then used to forward the packet to it’s final destination.

In the EoMPLS over GRE cases, the new IP header and GRE header will be removed from the packet at the tunnel destination and the MPLS (VC or VPN) label will be used to forward the packets to the appropriate L2 attachment circuit or L3 VRF.

The following scenarios describe the L2VPN and L3VPN over GRE deployment on provider edge (PE) or provider (P) routers:

PE to PE GRE Tunnels

In the PE to PE GRE tunnels scenario, a customer does not generally transition any part of the core to MPLS but prefers to offer EoMPLS and basic MPLS VPN services. Hence, GRE tunneling of the MPLS labeled traffic is done between PEs. This is the most common scenario seen in various customers networks.

P to P GRE Tunnels

The P to P GRE tunnels scenario is one where MPLS has been enabled between PE and P routers, but the network core may have non-MPLS-aware routers or IP encryption boxes. In this scenario, GRE tunneling of the MPLS labeled packets is done between P routers.

PE to P GRE Tunnels

The PE to P GRE tunnels scenario demonstrates a network where the P to P nodes are MPLS-aware, while GRE tunneling is done between a PE to P non MPLS network segment.

The following features are required for the deployment of scenarios described above:

GRE Specific:

Tunnel endpoints can be loopbacks or physical interfaces.

Configurable tunnel keepalive timer parameters per end point, and syslog message must be generated when the keepalive timer expires.

BFD support for tunnel failures and for IGPs using tunnels.

IGP loadsharing across GRE tunnels.

IGP redundancy across GRE tunnels.

Fragmentation across GRE tunnels.

Ability to pass jumbo frames.

Support for all IGP control plane traffic.

Support for IP TOS preservation across tunnel.

Tunnel should be independent of endpoint physical interface types such as POS, Gig, TenGig, and ATM.

Support for up to 100 GRE tunnels.

EoMPLS Specific:

Port mode EoMPLS.

VLAN mode EoMPLS.

Pseudowire redundancy.

AToM sequencing.

Tunnel selection--ability to map a specific pseudowire or pw-class to a GRE tunnel.

IGP loadsharing and redundancy. See below for more information.

Support for up to 200 EoMPLS VCs.

MPLS-VPN Specific:

Support for PE Role with IPv4 VRFs

Support for all PE-CE protocols

Load sharing through multiple tunnels and equal-cost IGP paths with a single tunnel

Support for redundancy via unequal-cost IGP paths with a single tunnel

Support for the IP Precedence value being copied onto the EXP bits field of the MPLS label, and then onto the Precedence bits on the outer IPv4 ToS field of the GRE packet.

Multipoint GRE Tunneling

Enhanced multipoint GRE (mGRE) tunneling technology provides a Layer 3 (L3) transport mechanism for use in IP networks. This same dynamic Layer 3 tunneling transport can be used within IP networks to transport VPN traffic across service provider and enterprise networks, as well as to provide interoperability for packet transport between IP and MPLS VPNs. This feature provides support for RFC 2547, which defines the outsourcing of IP-backbone services for enterprise networks.

Multipoint tunnels use the Next Hop Resolution Protocol (NHRP) in the same way that a Frame Relay multipoint interface uses information obtained by the reverse ARP mechanism to learn the Layer 3 addresses of the remote data-link connection identifiers (DLCIs).

In Cisco IOS Release 12.2(8)T and later releases, CEF-switching over mGRE tunnels was introduced. Previously, only process switching was available for mGRE tunnels. CEF-switching over mGRE tunnels enables CEF switching of IP traffic to and from multipoint GRE tunnels. Tunnel traffic can be forwarded to a prefix through a tunnel destination when both the prefix and the tunnel destination are specified by the application.

GRE CLNS Tunnel Support for IPv4 and IPv6 Packets

GRE tunneling of IPv4 and IPv6 packets through CLNS networks enables Cisco CLNS tunnels (CTunnels) to interoperate with networking equipment from other vendors. This feature provides compliance with RFC 3147.

The optional GRE services defined in header fields, such as checksums, keys, and sequencing, are not supported. Any packet that is received and requests such services will be dropped.

GRE IPv4 Tunnel Support for IPv6 Traffic

IPv6 traffic can be carried over IPv4 generic routing encapsulation (GRE) tunnels using the standard GRE tunneling technique that is designed to provide the services necessary to implement any standard point-to-point encapsulation scheme. As in IPv6 manually configured tunnels, GRE tunnels are links between two points, with a separate tunnel for each link. The tunnels are not tied to a specific passenger or transport protocol, but in this case, IPv6 is the passenger protocol, GRE is the carrier protocol, and IPv4 is the transport protocol.

The primary use of GRE tunnels is for stable connections that require regular secure communication between two edge routers or between an edge router and an end system. The edge routers and the end systems must be dual-stack implementations.

GRE has a protocol field that identifies the passenger protocol. GRE tunnels allow IS-IS or IPv6 to be specified as a passenger protocol, allowing both IS-IS and IPv6 traffic to run over the same tunnel. If GRE did not have a protocol field, it would be impossible to distinguish whether the tunnel was carrying IS-IS or IPv6 packets. The GRE protocol field is why it is desirable that you tunnel IS-IS and IPv6 inside GRE.

Overlay Tunnels for IPv6

Overlay tunneling encapsulates IPv6 packets in IPv4 packets for delivery across an IPv4 infrastructure (a core network or the Internet). (See the figure below.) By using overlay tunnels, you can communicate with isolated IPv6 networks without upgrading the IPv4 infrastructure between them. Overlay tunnels can be configured between border routers or between a border router and a host; however, both tunnel endpoints must support both the IPv4 and IPv6 protocol stacks. Cisco IOS IPv6 currently supports the following types of overlay tunneling mechanisms:

Manual

Generic routing encapsulation (GRE)

IPv4-compatible

6to4

Intra-Site Automatic Tunnel Addressing Protocol (ISATAP)

Figure 4. Overlay Tunnels

Note

Overlay tunnels reduce the maximum transmission unit (MTU) of an interface by 20 octets (assuming that the basic IPv4 packet header does not contain optional fields). A network that uses overlay tunnels is difficult to troubleshoot. Therefore, overlay tunnels that connect isolated IPv6 networks should not be considered as a final IPv6 network architecture. The use of overlay tunnels should be considered as a transition technique toward a network that supports both the IPv4 and IPv6 protocol stacks or just the IPv6 protocol stack.

Use the table below to help you determine which type of tunnel you want to configure to carry IPv6 packets over an IPv4 network.

Simple point-to-point tunnels that can be used within a site or between sites.

Can carry IPv6 packets only.

GRE/IPv4

Simple point-to-point tunnels that can be used within a site or between sites.

Can carry IPv6, CLNS, and many other types of packets.

Compatible

Point-to-multipoint tunnels.

Uses the ::/96 prefix. Currently, we do not recommend using this tunnel type.

6to4

Point-to-multipoint tunnels that can be used to connect isolated IPv6 sites.

Sites use addresses from the 2002::/16 prefix.

ISATAP

Point-to-multipoint tunnels that can be used to connect systems within a site.

Sites can use any IPv6 unicast addresses.

Individual tunnel types are discussed in more detail in the following concepts, and we recommend that you review and understand the information on the specific tunnel type that you want to implement. When you are familiar with the type of tunnel you need, the table below provides a quick summary of the tunnel configuration parameters that you may find useful.

Table 3 Overlay Tunnel Configuration Parameters by Tunneling Type

Overlay Tunneling Type

Overlay Tunnel Configuration Parameter

Tunnel Mode

Tunnel Source

Tunnel Destination

Interface Prefix/Address

Manual

ipv6ip

An IPv4 address or a reference to an interface on which IPv4 is configured.

An IPv4 address.

An IPv6 address.

GRE/IPv4

gre ip

An IPv4 address.

An IPv6 address.

Compatible

ipv6ip auto-tunnel

Not required. These are all point-to-multipoint tunneling types. The IPv4 destination address is calculated, on a per-packet basis, from the IPv6 destination.

Not required. The interface address is generated as ::tunnel-source/96.

6to4

ipv6ip 6to4

An IPv6 address. The prefix must embed the tunnel source IPv4 address.

ISATAP

ipv6ip isatap

An IPv6 prefix in modified eui-64 format. The IPv6 address is generated from the prefix and the tunnel source IPv4 address.

IPv6 Manually Configured Tunnels

A manually configured tunnel is equivalent to a permanent link between two IPv6 domains over an IPv4 backbone. The primary use is for stable connections that require regular secure communication between two edge routers or between an end system and an edge router, or for connection to remote IPv6 networks.

An IPv6 address is manually configured on a tunnel interface, and manually configured IPv4 addresses are assigned to the tunnel source and the tunnel destination. The host or router at each end of a configured tunnel must support both the IPv4 and IPv6 protocol stacks. Manually configured tunnels can be configured between border routers or between a border router and a host. CEF switching can be used for IPv6 manually configured tunnels, or CEF switching can be disabled if process switching is needed.

Automatic 6to4 Tunnels

An automatic 6to4 tunnel allows isolated IPv6 domains to be connected over an IPv4 network to remote IPv6 networks. The key difference between automatic 6to4 tunnels and manually configured tunnels is that the tunnel is not point-to-point; it is point-to-multipoint. In automatic 6to4 tunnels, routers are not configured in pairs because they treat the IPv4 infrastructure as a virtual nonbroadcast multiaccess (NBMA) link. The IPv4 address embedded in the IPv6 address is used to find the other end of the automatic tunnel.

An automatic 6to4 tunnel may be configured on a border router in an isolated IPv6 network, which creates a tunnel on a per-packet basis to a border router in another IPv6 network over an IPv4 infrastructure. The tunnel destination is determined by the IPv4 address of the border router extracted from the IPv6 address that starts with the prefix 2002::/16, where the format is 2002:border-router-IPv4-address
::/48. Following the embedded IPv4 address are 16 bits that can be used to number networks within the site. The border router at each end of a 6to4 tunnel must support both the IPv4 and IPv6 protocol stacks. 6to4 tunnels are configured between border routers or between a border router and a host.

The simplest deployment scenario for 6to4 tunnels is to interconnect multiple IPv6 sites, each of which has at least one connection to a shared IPv4 network. This IPv4 network could be the global Internet or a corporate backbone. The key requirement is that each site have a globally unique IPv4 address; the Cisco IOS software uses this address to construct a globally unique 6to4/48 IPv6 prefix. As with other tunnel mechanisms, appropriate entries in a Domain Name System (DNS) that map between hostnames and IP addresses for both IPv4 and IPv6 allow the applications to choose the required address.

Automatic IPv4-Compatible IPv6 Tunnels

Automatic IPv4-compatible tunnels use IPv4-compatible IPv6 addresses. IPv4-compatible IPv6 addresses are IPv6 unicast addresses that have zeros in the high-order 96 bits of the address and an IPv4 address in the low-order 32 bits. They can be written as 0:0:0:0:0:0:A.B.C.D or ::A.B.C.D, where "A.B.C.D" represents the embedded IPv4 address.

The tunnel destination is automatically determined by the IPv4 address in the low-order 32 bits of IPv4-compatible IPv6 addresses. The host or router at each end of an IPv4-compatible tunnel must support both the IPv4 and IPv6 protocol stacks. IPv4-compatible tunnels can be configured between border routers or between a border router and a host. Using IPv4-compatible tunnels is an easy method to create tunnels for IPv6 over IPv4, but the technique does not scale for large networks.

Note

IPv4-compatible tunnels were initially supported for IPv6, but are currently being deprecated. Cisco now recommends that you use a different IPv6 tunneling technique named ISATAP tunnels.

ISATAP Tunnels

The Intra-Site Automatic Tunnel Addressing Protocol (ISATAP) is an automatic overlay tunneling mechanism that uses the underlying IPv4 network as a nonbroadcast multiaccess (NBMA) link layer for IPv6. ISATAP is designed for transporting IPv6 packets within a site where a native IPv6 infrastructure is not yet available; for example, when sparse IPv6 hosts are deployed for testing. ISATAP tunnels allow individual IPv4/IPv6 dual-stack hosts within a site to communicate with other such hosts on the same virtual link, basically creating an IPv6 network using the IPv4 infrastructure.

The ISATAP router provides standard router advertisement network configuration support for the ISATAP site. This feature allows clients to automatically configure themselves as they would do if they were connected to an Ethernet. It can also be configured to provide connectivity out of the site. ISATAP uses a well-defined IPv6 address format composed of any unicast IPv6 prefix (/64), which can be link-local or global (including 6to4 prefixes), enabling IPv6 routing locally or on the Internet. The IPv4 address is encoded in the last 32 bits of the IPv6 address, enabling automatic IPv6-in-IPv4 tunneling.

While the ISATAP tunneling mechanism is similar to other automatic tunneling mechanisms, such as IPv6 6to4 tunneling, ISATAP is designed for transporting IPv6 packets within a site, not
between sites.

ISATAP uses unicast addresses that include a 64-bit IPv6 prefix and a 64-bit interface identifier. The interface identifier is created in modified EUI-64 format in which the first 32 bits contain the value 000:5EFE to indicate that the address is an IPv6 ISATAP address. The table below shows the layout of an ISATAP address.

Table 4 ISATAP address example

64 Bits

32 Bits

32 Bits

Link local or global IPv6 unicast prefix

0000:5EFE

IPv4 address of the ISATAP link

As shown in the table above, an ISATAP address consists of an IPv6 prefix and the ISATAP interface identifier. This interface identifier includes the IPv4 address of the underlying IPv4 link. The following example shows what an actual ISATAP address would look like if the prefix is 2001:0DB8:1234:5678::/64 and the embedded IPv4 address is 10.173.129.8. In the ISATAP address, the IPv4 address is expressed in hexadecimal as 0AAD:8108.

Example

2001:0DB8:1234:5678:0000:5EFE:0AAD:8108

Rate-Based Satellite Control Protocol Tunnels

Rate-Based Satellite Control Protocol (RBSCP) was designed for wireless or long-distance delay links with high error rates, such as satellite links. Using tunnels, RBSCP can improve the performance of certain IP protocols, such as TCP and IP Security (IPsec), over satellite links without breaking the end-to-end model.

Satellite links have several characteristics that affect the performance of IP protocols over the link. The figure below shows that satellite links can have a one-way delay of 275 milliseconds. A round-trip time (RTT) of 550 milliseconds is a very long delay for TCP. Another issue is the high error rates (packet loss rates) that are typical of satellite links as compared to wired links in LANs. Even the weather affects satellite links, causing a decrease in available bandwidth and an increase in RTT and packet loss.

Figure 5. Typical Satellite Link

Long RTT keeps TCP in a slow start mode, which increases the time before the satellite link bandwidth is fully used. TCP and Stream Control Transmission Protocol (SCTP) interpret packet loss events as congestion in the network and start to perform congestion recovery procedures, which reduce the traffic being sent over the link.

Although available satellite link bandwidths are increasing, the long RTT and high error rates experienced by IP protocols over satellite links are producing a high bandwidth-delay product (BDP).

To address the problem of TCP being kept in a slow start mode when a satellite link is used, a disruptive performance enhancing proxy (PEP) solution is often introduced into the network. In the figure below, you can see that the transport connection is broken up into three sections with hosts on the remote side connecting to the Internet through their default router. The router sends all Internet-bound traffic to the TCP PEP, which terminates the TCP connection to the Internet. The PEP generates a local TCP ACK (TCP spoofing) for all data. Traffic is buffered and retransmitted through a single PEP protocol connection over the satellite link. The second PEP receives the data from the satellite link and retransmits the data over separate TCP connections to the Internet. TCP transmission is disrupted, so dropped packets are not interpreted as TCP congestion and can be retransmitted from buffered data. Minimal TCP ACKs and reduced TCP slow starts allow more bandwidth to be used.

Figure 6. Disruptive TCP PEP Solution

One of the disadvantages to using disruptive TCP PEP is the breaking of the end-to-end model. Some applications cannot work when the flow of traffic is broken, and the PEP has no provision for handling encrypted traffic (IPsec). New transport protocols such as SCTP require special handling or additional code to function with disruptive TCP PEP. An additional managed network component is also required at every satellite router.

RBSCP has been designed to preserve the end-to-end model and provide performance improvements over the satellite link without using a PEP solution. IPsec encryption of clear-text traffic (for example a VPN service configuration) across the satellite link is supported. RBSCP allows two routers to control and monitor the sending rates of the satellite link, thereby increasing the bandwidth utilization. Lost packets are retransmitted over the satellite link by RBSCP, preventing the end host TCP senders from going into slow start mode.

RBSCP is implemented using a tunnel interface as shown in the figure below. The tunnel can be configured over any network interface supported by Cisco IOS software that can be used by a satellite modem or internal satellite modem network module. IP traffic is sent across the satellite link with appropriate modifications and enhancements that are determined by the router configuration. Standard routing or policy-based routing can be used to determine the traffic to be sent through the RBSCP tunnel.

Figure 7. Nondisruptive RBSCP Solution

RBSCP tunnels can be configured for any of the following features:

TimeDelay--One of the RBSCP routers can be configured to hold frames due for transmission through the RBSCP tunnel. The delay time increases the RTT at the end host and allows RBSCP time to retransmit lost TCP frames or other protocol frames. If the retransmission is successful, it prevents lost frame events from reaching the end host where congestion procedures would be enabled. In some cases, the retransmission can be completed by RBSCP without inserting the delay. This option should be used only when the RTT of the satellite link is greater than 700 milliseconds.

ACKSplitting--Performance improvements can be made for clear-text TCP traffic using acknowledgement (ACK) splitting in which a number of additional TCP ACKs are generated for each TCP ACK received. TCP will open a congestion window by one maximum transmission unit (MTU) for each TCP ACK received. Opening the congestion window results in increased bandwidth becoming available. Configure this feature only when the satellite link is not using all the available bandwidth. Encrypted traffic cannot use ACK splitting.

WindowStuffing--Clear-text TCP and SCTP traffic can benefit from the RBSCP window stuffing feature. RBSCP can buffer traffic so that the advertised window can be incremented up to the available satellite link bandwidth or the available memory in the router. The end host that sends the packets is fooled into thinking that a larger window exists at the receiving end host and sends more traffic. Use this feature with caution because the end host may send too much traffic for the satellite link to handle and the resulting loss and retransmission of packets may cause link congestion.

SCTPDropReporting--SCTP uses an appropriate byte counting method instead of ACK counting to determine the size of the transmission window, so ACK splitting does not work with SCTP. The RBSCP tunnel can generate an SCTP packet-dropped report for packets dropped across the satellite but not as a result of congestion loss. This SCTP drop reporting is on by default and provides a chance to retransmit the packet without affecting the congestion window size. Actual congestion losses are still reported, and normal recovery mechanisms are activated.

Path MTU Discovery

Path MTU Discovery (PMTUD) can be enabled on a GRE or IP-in-IP tunnel interface. When PMTUD (RFC 1191) is enabled on a tunnel interface, the router performs PMTUD processing for the GRE (or IP-in-IP) tunnel IP packets. The router always performs PMTUD processing on the original data IP packets that enter the tunnel. When PMTUD is enabled, packet fragmentation is not permitted for packets that traverse the tunnel because the Don’t Fragment (DF) bit is set on all the packets. If a packet that enters the tunnel encounters a link with a smaller MTU, the packet is dropped and an ICMP message is sent back to the sender of the packet. This message indicates that fragmentation was required (but not permitted) and provides the MTU of the link that caused the packet to be dropped.

PMTUD on a tunnel interface requires that the tunnel endpoint be able to receive ICMP messages generated by routers in the path of the tunnel. Check that ICMP messages can be received before using PMTUD over firewall connections.

Use the tunnelpath-mtu-discovery command to enable PMTUD for the tunnel packets, and use the showinterfacestunnel command to verify the tunnel PMTUD parameters. PMTUD currently works only on GRE and IP-in-IP tunnel interfaces.

QoS Options for Tunnels

A tunnel interface supports many of the same quality of service (QoS) features as a physical interface. QoS provides a way to ensure that mission-critical traffic has an acceptable level of performance. QoS options for tunnels include support for applying generic traffic shaping (GTS) directly on the tunnel interface and support for class-based shaping using the modular QoS CLI (MQC). Tunnel interfaces also support class-based policing, but they do not support committed access rate (CAR).

Note

Service policies are not supported on tunnel interfaces on the Cisco 7500 series routers.

GRE tunnels allow the router to copy the IP precedence bit values of the ToS byte to the tunnel or the GRE IP header that encapsulates the inner packet. Intermediate routers between the tunnel endpoints can use the IP precedence values to classify the packets for QoS features such as policy routing, weighted fair queueing (WFQ), and weighted random early detection (WRED).

When packets are encapsulated by tunnel or encryption headers, QoS features are unable to examine the original packet headers and correctly classify the packets. Packets that travel across the same tunnel have the same tunnel headers, so the packets are treated identically if the physical interface is congested. Tunnel packets can, however, be classified before tunneling and encryption can occur by using the QoS preclassify feature on the tunnel interface or on the crypto map.

Note

Class-based WFQ (CBWFQ) inside class-based shaping is not supported on a multipoint interface.

Determining the Tunnel Type

Before configuring a tunnel, you must determine what type of tunnel you need to create.

SUMMARY STEPS

1. Determine the passenger protocol.

2. Determine the tunnel CLI type.

3. Determine the
tunnelmode command keyword, if appropriate.

DETAILED STEPS

Step 1

Determine the passenger protocol.

The passenger protocol is the protocol that you are encapsulating.

Step 2

Determine the tunnel CLI type.

The table below shows how to determine the tunnel CLI command required for the transport protocol that you are using in the tunnel.

Table 5 Determining the Tunnel CLI by the Transport Protocol

Transport Protocol

Tunnel CLI Command

CLNS

ctunnel( with optional
modegre keywords)

Other

tunnelmode ( with appropriate keyword)

Step 3

Determine the
tunnelmode command keyword, if appropriate.

The table below shows how to determine the appropriate keyword to use with the
tunnelmode command. In the tasks that follow in this module, only the relevant keywords for the
tunnelmode command are displayed.

Table 6 Determining the tunnel mode Command Keyword

Keyword

Purpose

dvmrp

Use the
dvmrp keyword to specify that the Distance Vector Multicast Routing Protocol encapsulation will be used.

greip

Use the
greip keywords to specify that GRE encapsulation over IP will be used.

greipv6

Use the
greipv6 keywords to specify that GRE encapsulation over IPv6 will be used.

gremultipoint

Use the
gremultipoint keywords to specify that multipoint GRE (mGRE) encapsulation will be used.

ipip [decapsulate-any]

Use the
ipip keyword to specify that IP-in-IP encapsulation will be used. The optional
decapsulate-any keyword terminates any number of IP-in-IP tunnels at one tunnel interface. Note that this tunnel will not carry any outbound traffic; however, any number of remote tunnel endpoints can use a tunnel configured this way as their destination.

ipv6

Use the
ipv6 keyword to specify that generic packet tunneling in IPv6 will be used.

ipv6ip

Use the
ipv6ip keyword to specify that IPv6 will be used as the passenger protocol and IPv4 as both the carrier (encapsulation) and transport protocol. When additional keywords are not used, manual IPv6 tunnels are configured. Additional keywords can be used to specify IPv4-compatible, 6to4, or ISATAP tunnels.

mpls

Use the
mpls keyword to specify that MPLS will be used for configuring Traffic Engineering (TE) tunnels.

rbscp

Use the
rbscp keyword to specify that RBSCP tunnels will be used.

What to Do Next

To configure an RBSCP tunnel to carry IP data packets over a satellite
or other long-distance delay link with high error rates, proceed to the
Configuring the RBSCP Tunnel.

Configuring a GRE Tunnel

Perform this task to configure a GRE tunnel. A tunnel interface is used to pass protocol traffic across a network that does not normally support the protocol. To build a tunnel, a tunnel interface must be defined on each of two routers and the tunnel interfaces must reference each other. At each router, the tunnel interface must be configured with a L3 address. The tunnel endpoints, tunnel source, and tunnel destination must be defined, and the type of tunnel must be selected. Optional steps can be performed to customize the tunnel.

Remember to configure the router at each end of the tunnel. If only one side of a tunnel is configured, the tunnel interface may still come up and stay up (unless keepalive is configured), but packets going into the tunnel will be dropped.

In Cisco IOS Release 12.2(8)T and later releases, CEF-switching over multipoint GRE tunnels was introduced. Previously, only process switching was available for multipoint GRE tunnels.

GRE Tunnel Keepalive

Keepalive packets can be configured to be sent over IP-encapsulated GRE tunnels. You can specify the rate at which keepalives will be sent and the number of times that a device will continue to send keepalive packets without a response before the interface becomes inactive. GRE keepalive packets may be sent from both sides of a tunnel or from just one side.

Before You Begin

Ensure that the physical interface to be used as the tunnel source in this task is up and configured with the appropriate IP address. For hardware technical descriptions and information about installing interfaces, see the hardware installation and configuration publication for your product.

Note

GRE tunnel keepalive is not supported in cases where virtual route forwarding (VRF) is applied to a GRE tunnel.

>

SUMMARY STEPS

1.enable

2.configureterminal

3.interfacetypenumber

4.bandwidthkbps

5.keepalive[period [retries]]

6.tunnelsource{ip-address |
interface-typeinterface-number}

7.tunneldestination{hostname |
ip-address}

8.tunnelkeykey-number

9.tunnelmode{greip|
gremultipoint}

10.ipmtubytes

11.iptcpmssmss-value

12.tunnelpath-mtu-discovery[age-timer {aging-mins|
infinite}]

13.end

DETAILED STEPS

Command or Action

Purpose

Step 1

enable

Example:

Router> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2

configureterminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3

interfacetypenumber

Example:

Router(config)# interface tunnel 0

Specifies the interface type and number and enters interface configuration mode.

To configure a tunnel, use tunnel for the
type argument.

On some router platforms such as the Cisco 7500 series, the number argument may consist of a slot, port adapter, and port number. For more details, see the
interface command in the Cisco IOS Interface and Hardware Component Command Reference.

Step 4

bandwidthkbps

Example:

Router(config-if)# bandwidth 1000

Sets the current bandwidth value for an interface and communicates it to higher-level protocols. Specifies the tunnel bandwidth to be used to transmit packets.

Use the
kbpsargument to set the bandwidth, in kilobits per second (kbps).

Note

This is a routing parameter only; it does not affect the physical interface. The default bandwidth setting on a tunnel interface is 9.6 kbps. You should set the bandwidth on a tunnel to an appropriate value.

Step 5

keepalive[period [retries]]

Example:

Router(config-if)# keepalive 3 7

(Optional) Specifies the number of times that the device will continue to send keepalive packets without response before bringing the tunnel interface protocol down.

GRE keepalive packets may be configured either on only one side of the tunnel or on both.

If GRE keepalive is configured on both sides of the tunnel, the
period and
retries arguments can be different at each side of the link.

Note

This command is supported only on GRE point-to-point tunnels.

Step 6

tunnelsource{ip-address |
interface-typeinterface-number}

Example:

Router(config-if)# tunnel source Ethernet 1

Configures the tunnel source.

Use the
ip-addressargument to specify the source IP address.

Use the
interface-typeand
interface-numberarguments to specify the interface to use.

Note

The tunnel source and destination IP addresses must be defined on two separate devices.

Step 7

tunneldestination{hostname |
ip-address}

Example:

Router(config-if)# tunnel destination 172.17.2.1

Configures the tunnel destination.

Use the
hostnameargument to specify the name of the host destination.

Use the
ip-addressargument to specify the IP address of the host destination.

Note

The tunnel source and destination IP addresses must be defined on two separate devices.

Step 8

tunnelkeykey-number

Example:

Router(config-if)# tunnel key 1000

(Optional) Enables an ID key for a tunnel interface.

Use the
key-numberargument to identify a tunnel key that is carried in each packet.

Tunnel ID keys can be used as a form of weak security to prevent improper configuration or injection of packets from a foreign source.

Note

This command is supported only on GRE tunnel interfaces. We do not recommend relying on this key for security purposes.

Step 9

tunnelmode{greip|
gremultipoint}

Example:

Router(config-if)# tunnel mode gre ip

Specifies the encapsulation protocol to be used in the tunnel.

Use the
greip keywords to specify that GRE over IP encapsulation will be used.

Use the
gremultipoint keywords to specify that multipoint GRE (mGRE) will be used.

Step 10

ipmtubytes

Example:

Router(config-if)# ip mtu 1400

(Optional) Set the maximum transmission unit (MTU) size of IP packets sent on an interface.

If an IP packet exceeds the MTU set for the interface, the Cisco IOS software will fragment it unless the DF bit is set.

All devices on a physical medium must have the same protocol MTU in order to operate.

Note

If the
tunnelpath-mtu-discovery command is enabled in Step 12, do not configure this command.

Step 11

iptcpmssmss-value

Example:

Router(config-if)# ip tcp mss 250

(Optional) Specifies the maximum segment size (MSS) for TCP connections that originate or terminate on a router.

Use the
mss-value argument to specify the maximum segment size for TCP connections, in bytes.

What to Do Next

Configuring GRE IPv6 Tunnels

Perform this task to configure a GRE tunnel on an IPv6 network. GRE tunnels can be configured to run over an IPv6 network layer and transport IPv6 and IPv4 packets through IPv6 tunnels.

Before You Begin

When GRE IPv6 tunnels are configured, IPv6 addresses are assigned to the tunnel source and the tunnel destination. The tunnel interface can have either IPv4 or IPv6 addresses (this is not shown in the task below). The host or device at each end of the configured tunnel must support both IPv4 and IPv6 protocol stacks.

SUMMARY STEPS

1.enable

2.configureterminal

3.interfacetunneltunnel-number

4.tunnelsource{ipv6-address |
interface-typeinterface-number}

5.tunneldestinationipv6-address

6.tunnelmodegreipv6

7.end

DETAILED STEPS

Command or Action

Purpose

Step 1

enable

Example:

Device> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2

configureterminal

Example:

Device# configure terminal

Enters global configuration mode.

Step 3

interfacetunneltunnel-number

Example:

Device(config)# interface tunnel 0

Specifies a tunnel interface and number and enters interface configuration mode.

Step 4

tunnelsource{ipv6-address |
interface-typeinterface-number}

Example:

Device(config-if)# tunnel source ethernet 0

Specifies the source IPv6 address or the source interface type and number for the tunnel interface.

If an interface type and number are specified, the interface must be configured with an IPv6 address.

What to Do Next

Configuring a CTunnel

Perform this task to configure an IP over CLNS tunnel (CTunnel). To configure a CTunnel between a single pair of routers, a tunnel interface must be configured with an IP address, and a tunnel destination must be defined. The destination network service access point (NSAP) address for Router A would be the NSAP address of Router B, and the destination NSAP address for Router B would be the NSAP address of Router A. Ideally, the IP addresses used for the virtual interfaces at either end of the tunnel should be in the same IP subnet. Remember to configure the router at each end of the tunnel.

CTunnel

A CTunnel lets you transport IP traffic over Connectionless Network Service (CLNS), for example, on the data communications channel (DCC) of a SONET ring. CTunnels allow IP packets to be tunneled through the Connectionless Network Protocol (CLNP) to preserve TCP/IP services.

Configuring a CTunnel allows you to telnet to a remote router that has only CLNS connectivity. Other management facilities can also be used, such as Simple Network Management Protocol (SNMP) and TFTP, which otherwise would not be available over a CLNS network.

SUMMARY STEPS

1.enable

2.configureterminal

3.interfacectunnelinterface-number

4.ipaddressip-addressmask

5.ctunneldestinationremote-nsap-address

6.end

7.showinterfacesctunnelinterface-number

DETAILED STEPS

Command or Action

Purpose

Step 1

enable

Example:

Router> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2

configureterminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3

interfacectunnelinterface-number

Example:

Router(config)# interface ctunnel 102

Creates a virtual interface to transport IP over a CLNS tunnel and enters interface configuration mode.

Note

The interface number must be unique for each CTunnel interface.

Step 4

ipaddressip-addressmask

Example:

Router(config-if)# ip address 10.0.0.1 255.255.255.0

Enables IP on the interface.

Use the ip-addressand mask arguments to specify the IP address and mask for the interface.

Step 5

ctunneldestinationremote-nsap-address

Example:

Router(config-if)# ctunnel destination 49.0001.2222.2222.2222.00

Specifies the destination NSAP address of the CTunnel, where the packets exit the tunnel.

Use the remote-nsap-addressargument to specify the NSAP address at the CTunnel endpoint.

Troubleshooting Tips

What to Do Next

Configuring GRE CLNS CTunnels to Carry IPv4 and IPv6 Packets

Perform this task to configure a CTunnel in GRE mode to transport IPv4 and IPv6 packets in a CLNS network.

To configure a CTunnel between a single pair of routers, a tunnel interface must be configured with an IP address, and a tunnel destination must be defined. The destination network service access point (NSAP) address for Router A would be the NSAP address of Router B, and the destination NSAP address for Router B would be the NSAP address of Router A. Ideally, the IP addresses used for the virtual interfaces at either end of the tunnel should be in the same IP subnet. Remember to configure the router at each end of the tunnel.

Tunnels for IPv4 and IPv6 Packets over CLNS Networks

Configuring the
ctunnelmodegre command on a CTunnel interface enables IPv4 and IPv6 packets to be tunneled over CLNS in accordance with RFC 3147. Compliance with this RFC should allow interoperation between Cisco equipment and that of other vendors in which the same standard is implemented.

RFC 3147 specifies the use of GRE for tunneling packets. The implementation of this feature does not include support for GRE services defined in header fields, such as those used to specify checksums, keys, or sequencing. Any packets received that specify the use of these features will be dropped.

The default CTunnel mode continues to use the standard Cisco encapsulation, which will tunnel only IPv4 packets. If you want to tunnel IPv6 packets, you must use the GRE encapsulation mode. Both ends of the tunnel must be configured with the same mode for either method to work.

Before You Begin

An IPv4 or IPv6 address must be configured on a CTunnel interface, and manually configured CLNS addresses must be assigned to the CTunnel destination.

The host or router at each end of a configured CTunnel must support both the IPv4 and IPv6 protocol stacks.

The CTunnel source and destination must both be configured to run in the same mode.

Note

GRE services, such as those used to specify checksums, keys, or sequencing, are not supported. Packets that request use of those features will be dropped.

>

SUMMARY STEPS

1.enable

2.configureterminal

3.interfacectunnelinterface-number

4.Do one of the following:

ipaddressip-addressmask

ipv6addressipv6-prefix/prefix-length[eui-64]

5.ctunneldestinationremote-nsap-address

6.ctunnelmodegre

7.end

8.showinterfacesctunnelinterface-number

DETAILED STEPS

Command or Action

Purpose

Step 1

enable

Example:

Router> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2

configureterminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3

interfacectunnelinterface-number

Example:

Router(config)# interface ctunnel 102

Creates a virtual interface to transport IP over a CLNS tunnel and enters interface configuration mode.

Note

The interface number must be unique for each CTunnel interface.

Step 4

Do one of the following:

ipaddressip-addressmask

ipv6addressipv6-prefix/prefix-length[eui-64]

Example:

Router(config-if)# ipv6 address 2001:0DB8:1234:5678::3/126

Specifies the IPv4 or IPv6 network assigned to the interface and enables IPv4 or IPv6 packet processing on the interface.

Note

For more information about IPv6 network, see the "Configuring Basic Connectivity for IPv6" module in the Cisco IOS IPv6 Configuration Guide.

Step 5

ctunneldestinationremote-nsap-address

Example:

Router(config-if)# ctunnel destination 192.168.30.1

Specifies the destination NSAP address of the CTunnel, where the packets are extracted.

Use the
remote-nsap-addressargument to specify the NSAP address at the CTunnel endpoint.

Step 6

ctunnelmodegre

Example:

Router(config-if)# ctunnel mode gre

Specifies a CTunnel running in GRE mode for both IPv4 and IPv6 traffic.

Note

The
ctunnelmodegrecommand specifies GRE as the encapsulation protocol for the tunnel.

What to Do Next

Configuring Manual IPv6 Tunnels

This task explains how to configure a manual IPv6 overlay tunnel.

Before You Begin

With manually configured IPv6 tunnels, an IPv6 address is configured on a tunnel interface and manually configured IPv4 addresses are assigned to the tunnel source and the tunnel destination. The host or router at each end of a configured tunnel must support both the IPv4 and IPv6 protocol stacks.

SUMMARY STEPS

1.enable

2.configureterminal

3.interfacetunneltunnel-number

4.ipv6addressipv6-prefix/prefix-length[eui-64]

5.tunnelsource{ip-address|
interface-typeinterface-number}

6.tunneldestinationip-address

7.tunnelmodeipv6ip

8.end

DETAILED STEPS

Command or Action

Purpose

Step 1

enable

Example:

Router> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2

configureterminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3

interfacetunneltunnel-number

Example:

Router(config)# interface tunnel 0

Specifies a tunnel interface and number and enters interface configuration mode.

Step 4

ipv6addressipv6-prefix/prefix-length[eui-64]

Example:

Router(config-if)# ipv6 address 2001:0DB8:1234:5678::3/126

Specifies the IPv6 network assigned to the interface and enables IPv6 processing on the interface.

Note

For more information on configuring IPv6 addresses, see the "Configuring Basic Connectivity for IPv6" module.

Step 5

tunnelsource{ip-address|
interface-typeinterface-number}

Example:

Router(config-if)# tunnel source ethernet 0

Specifies the source IPv4 address or the source interface type and number for the tunnel interface.

If an interface is specified, the interface must be configured with an IPv4 address.

Step 6

tunneldestinationip-address

Example:

Router(config-if)# tunnel destination 192.168.30.1

Specifies the destination IPv4 address for the tunnel interface.

Step 7

tunnelmodeipv6ip

Example:

Router(config-if)# tunnel mode ipv6ip

Specifies a manual IPv6 tunnel.

Note

The
tunnelmodeipv6ip command specifies IPv6 as the passenger protocol and IPv4 as both the carrier (encapsulation) and transport protocol for the manual IPv6 tunnel.

What to Do Next

Configuring 6to4 Tunnels

This task explains how to configure a 6to4 overlay tunnel.

Before You Begin

With 6to4 tunnels, the tunnel destination is determined by the border-router IPv4 address, which is concatenated to the prefix 2002::/16 in the format 2002:border-router-IPv4-address::/48. The border router at each end of a 6to4 tunnel must support both the IPv4 and IPv6 protocol stacks.

Note

The configuration of only one IPv4-compatible tunnel and one 6to4 IPv6 tunnel is supported on a router. If you choose to configure both of these tunnel types on the same router, we strongly recommend that they not share the same tunnel source.

The reason that a 6to4 tunnel and an IPv4-compatible tunnel cannot share the same interface is that both of them are NBMA "point-to-multipoint" access links and only the tunnel source can be used to reorder the packets from a multiplexed packet stream into a single packet stream for an incoming interface. So when a packet with an IPv4 protocol type of 41 arrives on an interface, that packet is mapped to an IPv6 tunnel interface on the basis of the IPv4 address. However, if both the 6to4 tunnel and the IPv4-compatible tunnel share the same source interface, the router cannot determine the IPv6 tunnel interface to which it should assign the incoming packet.

IPv6 manually configured tunnels can share the same source interface because a manual tunnel is a "point-to-point" link, and both the IPv4 source and IPv4 destination of the tunnel are defined.

>

SUMMARY STEPS

1.enable

2.configureterminal

3.interfacetunneltunnel-number

4.ipv6addressipv6-prefix/prefix-length[eui-64]

5.tunnelsource{ip-address|
interface-typeinterface-number}

6.tunnelmodeipv6ip6to4

7.exit

8.ipv6routeipv6-prefix/prefix-lengthtunneltunnel-number

DETAILED STEPS

Command or Action

Purpose

Step 1

enable

Example:

Router> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2

configureterminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3

interfacetunneltunnel-number

Example:

Router(config)# interface tunnel 0

Specifies a tunnel interface and number and enters interface configuration mode.

Step 4

ipv6addressipv6-prefix/prefix-length[eui-64]

Example:

Router(config-if)# ipv6 address 2002:c0a8:6301:1::1/64

Specifies the IPv6 address assigned to the interface and enables IPv6 processing on the interface.

The 32 bits following the initial 2002::/16 prefix correspond to an IPv4 address assigned to the tunnel source.

Note

For more information about configuring IPv6 addresses, see the "Configuring Basic Connectivity for IPv6" module.

Step 5

tunnelsource{ip-address|
interface-typeinterface-number}

Example:

Router(config-if)# tunnel source ethernet 0

Specifies the source IPv4 address or the source interface type and number for the tunnel interface.

Note

The interface type and number specified in the
tunnelsource command must be configured with an IPv4 address.

What to Do Next

Configuring IPv4-Compatible IPv6 Tunnels

This task explains how to configure an IPv4-compatible IPv6 overlay tunnel.

Before You Begin

With an IPv4-compatible tunnel, the tunnel destination is automatically determined by the IPv4 address in the low-order 32 bits of IPv4-compatible IPv6 addresses. The host or router at each end of an IPv4-compatible tunnel must support both the IPv4 and IPv6 protocol stacks.

Note

IPv4-compatible tunnels were initially supported for IPv6, but Cisco now recommends that you use a different IPv6 overlay tunneling technique.

>

SUMMARY STEPS

1.enable

2.configureterminal

3.interfacetunneltunnel-number

4.tunnelsource{ip-address| interface-typeinterface-number}

5.tunnelmodeipv6ipauto-tunnel

DETAILED STEPS

Command or Action

Purpose

Step 1

enable

Example:

Router> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2

configureterminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3

interfacetunneltunnel-number

Example:

Router(config)# interface tunnel 0

Specifies a tunnel interface and number and enters interface configuration mode.

Step 4

tunnelsource{ip-address| interface-typeinterface-number}

Example:

Router(config-if)# tunnel source ethernet 0

Specifies the source IPv4 address or the source interface type and number for the tunnel interface.

Note

The interface type and number specified in the tunnelsource command must be configured with an IPv4 address.

Step 5

tunnelmodeipv6ipauto-tunnel

Example:

Router(config-if)# tunnel mode ipv6ip auto-tunnel

Specifies an IPv4-compatible tunnel using an IPv4-compatible IPv6 address.

What to Do Next

Configuring ISATAP Tunnels

This task describes how to configure an ISATAP overlay tunnel.

Before You Begin

The
tunnelsource command used in the configuration of an ISATAP tunnel must point to an interface that is configured with an IPv4 address. The ISATAP IPv6 address and prefix (or prefixes) advertised are configured for a native IPv6 interface. The IPv6 tunnel interface must be configured with a modified EUI-64 address because the last 32 bits in the interface identifier are constructed using the IPv4 tunnel source address.

SUMMARY STEPS

1.enable

2.configureterminal

3.interfacetunneltunnel-number

4.ipv6addressipv6-prefixprefix-length[eui-64]

5.noipv6ndsuppress-ra

6.tunnelsource{ip-address |
interface-typeinterface-number}

7.tunnelmodeipv6ipisatap

8.end

DETAILED STEPS

Command or Action

Purpose

Step 1

enable

Example:

Device> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2

configureterminal

Example:

Device# configure terminal

Enters global configuration mode.

Step 3

interfacetunneltunnel-number

Example:

Device(config)# interface tunnel 1

Specifies a tunnel interface and number and enters interface configuration mode.

Step 4

ipv6addressipv6-prefixprefix-length[eui-64]

Example:

Device(config-if)# ipv6 address 2001:0DB8:6301::/64 eui-64

Specifies the IPv6 address assigned to the interface and enables IPv6 processing on the interface.

Note

For more information on configuring IPv6 addresses, see the "Configuring Basic Connectivity for IPv6" module.

What to Do Next

Configuring the RBSCP Tunnel

Perform this task to configure the RBSCP tunnel. Remember to configure the router at each end of the tunnel.

Before You Begin

Ensure that the physical interface to be used as the tunnel source in this task is already configured.

Note

RBSCP was designed for wireless or long-distance delay links with high error rates such as satellite links. If you do not have long-distance delay links with high error rates, do not implement this feature.

If IP access control lists (ACLs) are configured on an interface that is used by an RBSCP tunnel, the RBSCP IP protocol (199) must be allowed to enter and exit that interface or the tunnel will not function.

RBSCP has some performance limitations because traffic through the tunnel is process-switched.

>

SUMMARY STEPS

1.enable

2.configureterminal

3.interfacetypenumber

4.ipunnumberedinterface-typeinterface-number

5.tunnelsource{ip-address | interface-typeinterface-number}

6.tunneldestination{hostname | ip-address}

7.tunnelbandwidth{receive | transmit}bandwidth

8.tunnelmoderbscp

9.tunnelrbscpack-splitsplit-size

10.tunnelrbscpdelay

11.tunnelrbscpreport

12.tunnelrbscpwindow-stuffstep-size

13.end

DETAILED STEPS

Command or Action

Purpose

Step 1

enable

Example:

Router> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2

configureterminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3

interfacetypenumber

Example:

Router(config)# interface tunnel 0

Specifies the interface type and number and enters interface configuration mode.

Step 4

ipunnumberedinterface-typeinterface-number

Example:

Router(config-if)# ip unnumbered Ethernet 1

Enables IP processing on an interface without assigning an explicit IP address.

Whenever the unnumbered interface generates a packet (for example, for a routing update), it uses the address of the specified interface as the source address of the IP packet.

Step 5

tunnelsource{ip-address | interface-typeinterface-number}

Example:

Router(config-if)# tunnel source Ethernet 1

Configures the tunnel source.

Use the ip-addressargument to specify the IP address of the service provider.

Use the interface-typeand interface-numberarguments to specify the interface to use. For RBSCP Cisco recommends specifying an interface as the tunnel source.

Step 6

tunneldestination{hostname | ip-address}

Example:

Router(config-if)# tunnel destination 172.17.2.1

Configures the tunnel destination.

Use the hostnameargument to specify the name of the host destination.

Use the ip-addressargument to specify the IP address of the host destination.

Step 7

tunnelbandwidth{receive | transmit}bandwidth

Example:

Router(config-if)# tunnel bandwidth transmit 1000

Specifies the tunnel bandwidth to be used to transmit packets.

Use the bandwidthargument to specify the bandwidth.

Note

The receive keyword is no longer used.

Step 8

tunnelmoderbscp

Example:

Router(config-if)# tunnel mode rbscp

Specifies the protocol to be used in the tunnel.

Use the rbscp keyword to specify that RBSCP will be used as the tunnel protocol.

Use the split-size argument to specify the number of ACKs to send for every ACK received.

The default number of ACKs is 4.

Step 10

tunnelrbscpdelay

Example:

Router(config-if)# tunnel rbscp delay

(Optional) Enables RBSCP tunnel delay.

Use this command only when the RTT measured between the two routers nearest to the satellite links is greater than 700 milliseconds.

Step 11

tunnelrbscpreport

Example:

Router(config-if)# tunnel rbscp report

(Optional) Reports dropped RBSCP packets to SCTP.

Reporting dropped packets to SCTP provides better bandwidth use because RBSCP tells the SCTP implementation at the end hosts to retransmit the dropped packets and this prevents the end hosts from assuming that the network is congested.

Verifying Tunnel Configuration and Operation

This optional task explains how to verify tunnel configuration and operation. The commands contained in the task steps can be used in any sequence and may need to be repeated. The following commands can be used for GRE tunnels, IPv6 manually configured tunnels, and IPv6 over IPv4 GRE tunnels. This process includes the following general steps (details follow):

On Router A, ping the IP address of the CTunnel interface of Router B.

On Router B, ping the IP address of the CTunnel interface of Router A.

SUMMARY STEPS

1.enable

2.showinterfacestunnelnumber[accounting]

3.ping [protocol]destination

4.showiproute[address[mask]]

5.ping [protocol]destination

DETAILED STEPS

Step 1

enable

Enables privileged EXEC mode. Enter your password if prompted.

Example:

Router> enable

Step 2

showinterfacestunnelnumber[accounting]

Assuming a generic example suitable for both IPv6 manually configured tunnels and IPv6 over IPv4 GRE tunnels, two routers are configured to be endpoints of a tunnel. Router A has Ethernet interface 0/0 configured as the source for tunnel interface 0 with an IPv4 address of 10.0.0.1 and an IPv6 prefix of 2001:0DB8:1111:2222::1/64. Router B has Ethernet interface 0/0 configured as the source for tunnel interface 1 with an IPv4 address of 10.0.0.2 and an IPv6 prefix of 2001:0DB8:1111:2222::2/64.

To verify that the tunnel source and destination addresses are configured, use the showinterfacestunnel command on Router A.

Example Configuring GRE IPv4 Tunnels

The following example shows a simple configuration of GRE tunneling. Note that Ethernet interface 0/1 is the tunnel source for Router A and the tunnel destination for Router B. Fast Ethernet interface 0/1 is the tunnel source for Router B and the tunnel destination for Router A.

Example: Configuring GRE IPv6 Tunnels

The following example shows how to configure a GRE tunnel over an IPv6 transport. In this example, Ethernet0/0 has an IPv6 address, and this is the source address used by the tunnel interface. The destination IPv6 address of the tunnel is specified directly. In this example, the tunnel carries both IPv4 and IS-IS traffic.

Example Configuring GRE CLNS CTunnels to Carry IPv4 and IPv6 Packets

The following example configures a GRE CTunnel running both IS-IS and IPv6 traffic between Router A and Router B in a CLNS network. The ctunnelmodegre command provides a method of tunneling that is compliant with RFC 3147 and should allow tunneling between Cisco equipment and third-party networking devices.

To turn off GRE mode and restore the CTunnel to the default Cisco encapsulation routing only between endpoints on Cisco equipment, use either the noctunnelmode command or the ctunnelmodecisco command. The following example shows the same configuration modified to transport only IPv4 traffic.

Example Configuring Manual IPv6 Tunnels

The following example configures a manual IPv6 tunnel between Router A and Router B. In the example, tunnel interface 0 for both Router A and Router B is manually configured with a global IPv6 address. The tunnel source and destination addresses are also manually configured.

Router B

Example Configuring 6to4 Tunnels

The following example configures a 6to4 tunnel on a border router in an isolated IPv6 network. The IPv4 address is 192.168.99.1, which translates to the IPv6 prefix of 2002:c0a8:6301::/48. The IPv6 prefix is subnetted into 2002:c0a8:6301::/64 for the tunnel interface: 2002:c0a8:6301:1::/64 for the first IPv6 network and 2002:c0a8:6301:2::/64 for the second IPv6 network. The static route ensures that any other traffic for the IPv6 prefix 2002::/16 is directed to tunnel interface 0 for automatic tunneling.

Example Configuring IPv4-Compatible IPv6 Tunnels

The following example configures an IPv4-compatible IPv6 tunnel that allows BGP to run between a number of routers without having to configure a mesh of manual tunnels. Each router has a single IPv4-compatible tunnel, and multiple BGP sessions can run over each tunnel, one to each neighbor. Ethernet interface 0 is used as the tunnel source. The tunnel destination is automatically determined by the IPv4 address in the low-order 32 bits of an IPv4-compatible IPv6 address. Specifically, the IPv6 prefix 0:0:0:0:0:0 is concatenated to an IPv4 address (in the format 0:0:0:0:0:0:A.B.C.D or ::A.B.C.D) to create the IPv4-compatible IPv6 address. Ethernet interface 0 is configured with a global IPv6 address and an IPv4 address (the interface supports both the IPv6 and IPv4 protocol stacks).

Multiprotocol BGP is used in the example to exchange IPv6 reachability information with the peer 10.67.0.2. The IPv4 address of Ethernet interface 0 is used in the low-order 32 bits of an IPv4-compatible IPv6 address and is also used as the next-hop attribute. Using an IPv4-compatible IPv6 address for the BGP neighbor allows the IPv6 BGP session to be automatically transported over an IPv4-compatible tunnel.

Example Configuring Routing for the RBSCP Tunnel

To control the type of traffic that uses the RBSCP tunnel, you must configure the appropriate routing. If you want to direct all traffic through the tunnel, you can configure a static route.

Note

To prevent routing flaps, remember to configure the tunnel interface as passive if dynamic routing protocols are used.

The following example shows how to use policy-based routing to route some specific protocol types through the tunnel. In this example, an extended access list allows TCP, Stream Control Transmission Protocol (SCTP), Encapsulating Security Payload (ESP) protocol, and Authentication Header (AH) traffic to travel through the tunnel. All IP traffic is denied.

Example Configuring QoS Options on Tunnel Interfaces

The following sample configuration applies generic traffic shaping (GTS) directly on the tunnel interface. In this example the configuration shapes the tunnel interface to an overall output rate of 500 kbps. For more details on GTS, see the " Regulating Packet Flow Using Traffic Shaping " chapter of the Cisco IOS Quality of Service Solutions Configuration Guide.

The following sample configuration shows how to apply the same shaping policy to the tunnel interface with the Modular QoS CLI (MQC) commands. For more details on MQC, see the "Modular Quality of Service Command-Line Interface" chapter of the Cisco IOS Quality of Service Solutions Configuration Guide .

Policing Example

When an interface becomes congested and packets start to queue, you can apply a queueing method to packets that are waiting to be transmitted. Cisco IOS logical interfaces--tunnel interfaces in this example--do not inherently support a state of congestion and do not support the direct application of a service policy that applies a queueing method. Instead, you need to apply a hierarchical policy. Create a "child" or lower-level policy that configures a queueing mechanism, such as low latency queueing with the
priority command and class-based weighted fair queueing (CBWFQ) with the
bandwidth command.

policy-map child
class voice
priority 512

Create a "parent" or top-level policy that applies class-based shaping. Apply the child policy as a command under the parent policy because admission control for the child class is done according to the shaping rate for the parent class.

IANA Allocation Guidelines for Values in the Internet Protocol and Related Headers

RFC 2784

Generic Routing Encapsulation (GRE)

RFC 2890

Key and Sequence Number Extensions to GRE

RFC 2893

Transition Mechanisms for IPv6 Hosts and Routers

RFC 3056

Connection of IPv6 Domains via IPv4 Clouds

RFC 3147

Generic Routing Encapsulation over CLNS Networks

Technical Assistance

Description

Link

The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password.

Feature Information for Implementing Tunnels

The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to
www.cisco.com/​go/​cfn. An account on Cisco.com is not required.

Table 7 Feature Information for Implementing Tunnels

Feature Name

Releases

Feature Configuration Information

CEF-Switched Multipoint GRE Tunnels

12.2(8)T

15.0(1)M

The CEF-Switched Multipoint GRE Tunnels feature enables CEF switching of IP traffic to and from multipoint GRE tunnels. Tunnel traffic can be forwarded to a prefix through a tunnel destination when both the prefix and the tunnel destination are specified by the application.

This feature introduces CEF switching over multipoint GRE tunnels. Previously, only process switching was available for multipoint GRE tunnels.

No commands were introduced or modified by this feature.

CLNS Support for GRE Tunneling of IPv4 and IPv6 Packets in CLNS Networks

12.3(7)T

12.2(25)S

12.2(33)SRA

Support of the GRE tunnel mode allows Cisco CTunnels to transport IPv4 and IPv6 packets over CLNS-only networks in a manner that allows interoperation between Cisco networking equipment and that of other vendors. This feature provides compliance with RFC 3147.

The following command was introduced by this feature:
ctunnelmode.

GRE Tunnel IP Source and Destination VRF Membership

12.0(23)S

12.2(20)S

12.2(27)SBC

12.3(2)T

12.2(33)SRA

12.2(33)SRB

12.2(31)SB5

12.4(15)T

Allows you to configure the source and destination of a tunnel to belong to any VPN VRF table.

In 12.0(23)S, this feature was introduced.

In 12.2(20)S this feature became available on Cisco 7304 router using the NSE-100 in the PXF processing path.

In 12.2(31)SB5, support was added for the Cisco 10000 series router for the PRE2 and PRE3.

The following command was introduced to support this feature:
tunnelvrf.

GRE Tunnel Keepalive

12.2(8)T

12.0(23)S

15.0(1)M

Cisco IOS XE 3.1.0SG

15.3(1)S

15.1(2)SY

The GRE Tunnel Keepalive feature provides the capability of configuring keepalive packets to be sent over IP-encapsulated generic routing encapsulation (GRE) tunnels. You can specify the rate at which keepalives will be sent and the number of times that a device will continue to send keepalive packets without a response before the interface becomes inactive. GRE keepalive packets may be sent from both sides of a tunnel or from just one side.

The following command was introduced by this feature:
keepalive (tunnel interfaces).

IP Tunnel-- SSO

15.1(1)SY

High availability support was added to IP Tunnels.

No new commands were introduced or modified by this feature.

Rate-Based Satellite Control Protocol

12.3(7)T

Rate-Based Satellite Control Protocol (RBSCP) was designed for wireless or long-distance delay links with high error rates, such as satellite links. Using tunnels, RBSCP can improve the performance of certain IP protocols, such as TCP and IP Security (IPSec), over satellite links without breaking the end-to-end model.

The following commands were introduced or modified by this feature:
clearrbscp,debugtunnelrbscp,showrbscp,tunnelbandwidth,tunnelmode,tunnelrbscpack-split,tunnelrbscpdelay,tunnelrbscpinput-drop,tunnelrbscplong-drop,tunnelrbscpreport,tunnelrbscpwindow-stuff.

Tunnel ToS

12.0(17)S

12.0(17)ST

12.2(8)T

12.2(14)S

15.0(1)M

The Tunnel ToS feature allows you to configure the ToS and Time-to-Live (TTL) byte values in the encapsulating IP header of tunnel packets for an IP tunnel interface on a router. The Tunnel ToS feature is supported on Cisco Express Forwarding (CEF), fast switching, and process switching forwarding modes.

The following commands were introduced or modified by this feature:
showinterfacestunnel,
tunneltos,
tunnelttl.